(navigation image)
Home American Libraries | Canadian Libraries | Universal Library | Community Texts | Project Gutenberg | Children's Library | Biodiversity Heritage Library | Additional Collections
Search: Advanced Search
Anonymous User (login or join us)
Upload
See other formats

Full text of "Improved quality of retail beef through control of bacterial spoilage."

■ ^u Agriculture 



Canada 

Research Direction generate 
Branch de la recherche 



Technical Bulletin 1984— 13E 




Improved quality of retail 
beef through control of 
bacterial spoilage 




Canada 



[Tie map on the cover has dots representing 
Agriculture Canada research establishments. 



Improved quality of retail 
beef through control of 
bacterial spoilage 



G. GORDON GREER 

Agriculture Canada 
Research Station 
Lacombe, Alberta 



Research Branch 
Agriculture Canada 
1984 



Copies of this publication are available from: 

Director 

Research Station 

Research Branch 

Agriculture Canada 

Lacombe, Alberta 

TOC ISO 

Produced by Research Program Service 

©Minister of Supply and Services Canada 1984 
Cat. No. A54— 8/1984— 13E 
ISBN 0-662-13396-X 

Egalement disponible en franc.ais sous le titre 
Proliferation des bacteries et qualite du 
boeuf au detail 



SUMMARY 

The retail case life of fresh beef is usually limited to 2 to 3 days due 
to the development of undesirable surface discoloration. This reduction in 
color acceptability has been shown to be related to the growth of psychrotro- 
phic bacteria at the meat surface. The retailer can improve the keeping 
quality of beef by reducing the number of bacteria initially contaminating the 
meat and by controlling the growth of organisms which are present. Although 
the application of a rigorous program of retail sanitation will reduce the 
initial numbers of bacteria transferred to the meat surface the retailer has 
no control over the bacterial quality of carcasses or wholesale product re- 
ceived from the supplier. In this regard it has been shown that the level of 
contamination on wholesale cuts is more than one and one half times as impor- 
tant as retail sanitation in determining the case life of retail beef. 

The nature of the retail display environment is such that beef is subjected 
to considerable temperature abuse resulting in limited case life. The following 
two practical methods of retail temperature control have been proposed 1) re- 
moval of beef from the retail case at the end of each work day and storage in a 
walk-in cooler overnight 2) a reduction in retail case temperature to maintain 
meat surface temperatures just above the freezing point. The application of 
these methods has been shown to result in a substantial increase in retail case 
life which would be economically beneficial to the retail beef industry. Also, 
proper retail temperature control should increase consumer satisfaction follow- 
ing meat purchases due to improved keeping quality in home refrigerators. 



RESUME 

La duree de conservation du boeuf frais en etalage chez le detaillant se 
limite habituellement a deux ou trois jours en raison du brunissement 
progressif de la viande en surface. II a ete demontre que cette alteration de 
la viande est causee par la proliferation de bacteries psychrotrophes en 
surface. Le detaillant peut accroitre la duree de conservation du boeuf en 
reduisant le nombre initial de bacteries qui contaminent la viande et en 
freinant la croissance des organismes presents. Cependant, bien qu'il puisse 
reduire le nombre de bacteries transmises a la surface de la viande en 
appliquant un programme d'assainisseraent rigoureux, il ne peut exercer aucun 
controle sur la qualite bacteriologique des carcasses ou des produits de gros 
qu'il regoit du fournisseur. II a ete demontre qu'a l'egard de la 
determination de la duree de conservation du boeuf en etalage le degre de 
contamination des morceaux de gros est plus d'une fois et demie plus important 
que les mesures sanitaires appliquees chez le detaillant. 

Le mode d' etalage des viandes chez le detaillant est tel que le boeuf est 
expose a des exces de temperature qui reduisent sa duree de conservation. On 
propose deux methodes de controle de la temperature a laquelle est exposee la 
viande: . soit retirer la'viande du comptoir a la fin de la journee et la 
conserver dans une chambre froide au cours de la nuit, soit reduire la 
temperature des comptoirs a viande de facon a maintenir la surface de la 
viande a des temperatures juste au-dessus du point de congelation. II a ete 
prouve que l 1 application de ces mesures entraine une augmentation 
substantielle de la duree de conservation de la viande au comptoir ce qui 
serait economiquement profitable au secteur du boeuf au detail. En outre, le 
controle adequat des temperatures de la viande vendue au detail devrait 
accroitre la satisfaction des consommateurs, ces derniers obtenant en effet 
des viandes se conservant plus longtemps. 



CONTENTS 

INTRODUCTION 1 

SOURCES OF BACTERIAL CONTAMINATION 1 

BACTERIA AND RETAIL BEEF SPOILAGE 2 

BACTERIAL GROWTH, BEEF SURFACE DISCOLORATION AND RETAIL CASE LIFE .... 5 

CONTROL OF RETAIL BEEF SPOILAGE 7 

Sanitation 7 

Temperature 9 

Methods of Retail Temperature Control 13 



- 1 - 



INTRODUCTION 

Fresh, retail beef is conveniently displayed in illuminated, self-serve, 
refrigerated cabinets to facilitate consumer evaluation prior to purchase. 
Under these conditions, however, the quality of beef rapidly deteriorates and 
seldom remains acceptable for more than 2 to 3 days. It is the growth of 
bacteria on the meat surface which produces undesirable odors, slime, and sur- 
face discoloration making the product unacceptable to the consumer. As a con- 
sequence, if retail beef is not purchased within a relatively short time the 
retailer suffers considerable spoilage losses. It has recently been estimated 
that losses due to bacterial spoilage can be in excess of $24,000 per year for 
a single retail store. In view of the magnitude of these losses methods of 
controlling these detrimental spoilage bacteria are of prime importance to the 
retailer. 

Although the retailer has no control over the level of contamination which 
accumulates during the pre-retail, primary, meat processing stages he has the 
potential to exert the final control on quality. Since the retailer occupies 
this key position it is necessary that he be knowledgeable of bacterial-induced 
spoilage and measures which can be applied to improve the keeping quality of 
retail meats. The intent of this overview is to outline the characteristics of 
bacteria relevant to beef spoilage and to recommend practical procedures by 
which bacterial growth can be retarded and retail case life substantially ex- 
tended. 

SOURCES OF BACTERIAL CONTAMINATION 

There is sufficient evidence to conclude that the unexposed muscle tissues 
of healthy beef cattle are free from spoilage bacteria. However, the soiled 
hides, hooves and expelled faeces of slaughtered animals are the initial sources 
of carcass contamination throughout the various primary processing stages at the 
abattoir. Bacterial contamination from these sources is spread to the carcass 
surface via contact with knives, saws and meat handlers during carcass dressing 
and cooling. Increased handling during carcass breaking, the fabrication of 
primal and subprimal cuts and transport contributes significantly to the level 
of contamination. Thus, the ultimate bacterial quality of carcasses or whole- 
sale cuts received by the retailer reflects the cumulative effects of processing 
contamination from slaughter to receipt at the retail store. 

At the retail store, the retailer must contend with carcasses or wholesale 
product of unknown bacterial quality. It is unfortunate that the degree of 
contamination on the surface of this starting material provides a major reservoir 
for the bacterial contamination of the freshly exposed surfaces of retail beef. 
However, the retailer can, through frequent sanitization, reduce the levels of 
bacteria contaminating work surfaces, and the hands and apparel of meat cutters. 
In this regard, it has been shown that the implementation of a rigid retail 
sanitation program can result in an economically beneficial extension of beef 
retail case life. The relative contribution of wholesale and retail contamina- 
tion to beef case life will be discussed further in a subsequent section. 



- 2 - 



BACTERIA AND RETAIL BEEF SPOILAGE 

The presence of glucose, soluble nitrogen-containing compounds, vitamins, 
minerals and a high moisture content makes fresh beef a highly nutritious 
medium readily supporting the growth of a number of bacterial species. From 
the standpoint of spoilage, the bacteria of concern to the industry are those 
whose growth results in esthetically undesirable changes in product quality. 
Since fresh beef is subjected to continuous refrigeration during processing 
and throughout retail display, these spoilage organisms must be able to survive 
and grow at low temperatures. Appropriately, the term psychrotroph, meaning 
"cold-thriving" or "cold-increasing" has been adopted to describe species of 
bacteria capable of growth at 5°C and below. The predominant psychrotrophic 
bacteria associated with aerobically spoiled beef, other red meats and poultry 
are members of the genus Pseudomonas . These small rod-shaped bacteria (Fig. 1) 
are not harmful to man but their growth and metabolic activities at the meat 
surface results in discoloration, off-odors, slime formation and undesirable 
flavors. It should be stressed, that with the exception of extremely advanced 
stages of beef spoilage bacterial growth is restricted to the outer few 
millimeters of the meat surface. In the case of ground beef, however, spoilage 
bacteria are distributed throughout the product during grinding. 







Fig. 1 . These small bacteria growing on the surface of beef reduce retail 
case life. Bacteria were isolated from the surface of spoiled rib- 
eye steaks, stained and magnified 3,000 x using a light microscope, 










A 




■ 



Fig. 2. The progressive increase in the undesirable brown surface discoloration on steaks 
results in spoilage losses. 



- 5 - 




Fig, 3 The amount of steak surface discoloration is dependent upon the 
number of bacteria growing on the meat surface. Bacteria 
appearing on the culture plates 1 to 7 were isolated from the 
steaks depicted in Fig. 2.1 to 2.7, respectively. 



Of the bacteria-related sensory changes occurring in overwrapped, retail 
beef cuts, surface discoloration is the most relevant. Relative to this, it 
is the first alteration in product quality which becomes evident in the time 
course of spoilage. Off-odors, objectionable flavors and slime are not 
apparent until much later and odors and flavors cannot be evaluated until the 
meat has been purchased, opened and/or prepared for consumption in the home. 
Furthermore, studies have shown that color is one of the major quality attri- 
butes influencing consumer selection of retail beef. If there are significant 
deviations from the acceptable color of fresh beef, the meat becomes 
unacceptable to the consumer and the retailer incurs losses. 



BACTERIAL GROWTH, BEEF SURFACE DISCOLORATION AND RETAIL CASE LIFE 

In view of the importance of color to beef acceptability, the extent of 
bacterial-induced surface discoloration can be used as a measure of retail 
beef case life. As bacteria grow on the meat surface they accelerate the 
oxidation of meat pigments which results in a progressive deterioration of the 



- 6 - 

acceptable red color (Fig. 2.1) and the appearance of varying degrees of brown 
surface discoloration (Fig. 2.1 to 2.7) until the steak is completely dis- 
colored (Fig. 2 7). When the rib-eye steaks depicted in Fig. 2 were sampled, 
and cultured on a suitable nutrient medium and incubated for a specified period 
of time, small colonies of bacteria appeared (Fig. 3). Although the steak 
exhibiting no surface discoloration (Fig. 2.1) contains relatively few bacteria 
(Fig. 3.1) as the extent of steak surface discoloration increases (Fig. 2.2 to 
2.7) there is a substantial increase in the number of bacteria which can be 
isolated from the steak surface (Fig. 3.2 to 3.7). It should be re-emphasized 
that the relationship between bacterial numbers and surface discoloration is 
based upon psychrotrophic counts obtained following incubation at 7°C for 10 
days. 

The number of bacteria present on the meat surface can be estimated by 
counting colonies on culture media such as those depicted in Fig. 3. By 
sampling steaks on a daily basis and determining bacterial numbers it is 
possible to construct a bacterial growth curve. At the same time the 
appearance of steaks can be evaluated by a sensory panel and scored for the 
extent of surface discoloration and overall retail acceptance. In the labora- 
tory, 7-point sensory scales are routinely used to evaluate both discoloration 
(1 = no discoloration, 7 = complete discoloration) and retail acceptance 
(1 = extremely undesirable; 7 = extremely desirable). The data presented in 
Figs. 4 and 5 show bacterial growth, steak surface discoloration and retail 
acceptance for 50 rib-eye steaks displayed for up to 4 days under simulated 
retail conditions. Initially, it is evident that the onset and rate of steak 
surface discoloration closely parallels that of bacterial growth (Fig. 4). 




complete 
discolouration 

-7 



r 

1 2 3 

TIME ON Dl SPLAY (DAYS) 



Z 

52 



4 no 
disco louration 



Fig. 4 . The increase in the extent of steak surface discoloration (" 
closely follows the growth of bacteria on the steak surface 
during retail display. 



- 7 - 



Furthermore, as the degree of steak surface discoloration progressively in- 
creases there is a concomitant decrease in the acceptability of retail steaks 
(Fig. 5). Thus, the extent of psychrotrophic bacterial-induced surface dis- 
coloration is the major factor limiting the shelf life of retail beef. 
Additional analyses of the data in Figs. 4 and 5 showed that if retail steaks 
have an initial bacterial load of about 1,000 bacteria/cm^ they will become 
visually unacceptable within 2.5 days of retail display at which time bacterial 
numbers would approximate 1,000, OOO/cm^ on the meat surface. It is noteworthy 
that this retail case life, determined in the laboratory, is in accordance with 
the 2 to 3 day case life reported under actual retail conditions. 



complete 



7t 



04 

o 



E3- 



2 



discolourat ion 



extremely 
desirable , 



6 



no o 
discolourat ion 



5u 

z 



4IM 
(J 

o 
< 



"3 



-2 



1-1 



TIME ON DISPLAY (DAYS) 



4 extremely 
undesirable 



Fig. 5 . The progressive decrease in the retail acceptance of steaks (minimi) 
is due to increased surface discoloration ( ■■^■^■^■■w) . 



CONTROL OF RETAIL BEEF SPOILAGE 



Sanitation 



The case life of fresh beef is directly related to the initial number of 
psychrotrophic bacteria associated with the surface of retail cuts when they 
are first wrapped and placed in the retail display case. At low levels of con- 
tamination (10 bacteria/cm^) case life will exceed 3 days, but with every 10-fold 



increase in the initial bacterial load there is a corresponding two-fifths of 
a day decrease in case life and at bacterial loads approaching 10°/cm , case 
life is less than 1 day (Fig. 6). In view of this, the retailer must 
frequently sanitize knives, saws, cutting tables, grinders and the floors and 
walls of the cutting area to reduce the numbers of bacteria, transferred to 
the meat during the processing of retail cuts. The repeated use of suitable 
germicidal hand washes is also recommended to reduce the microflora associated 
with the hands of meat cutters. Actual retail store case studies have shown 
that an economically beneficial increase in meat case life can result from the 
application of a rigid sanitation program at the retail level. 



i 



n- 



— 



i ' i i i 

4 5 6 7 8 

10 10 10 10 10 10 10 10 

INITIAL LOAD ( PS YC H ROT R OP H I C BACTERIA/CM ) 



Fig. 6 . As the number of psychrotrophic bacteria initially contaminating steaks 
increases there is a decrease in retail case life. 



As cited earlier, an additional source of contamination for retail beef 
cuts is the surface of carcasses and wholesale product received by the retailer. 
The retailer has no control over the bacterial quality of this starting material 
and bacteria are readily transferred to the freshly cut meat surfaces during the 
fabrication of retail cuts. In the laboratory, studies were designed and con- 
ducted to determine the relative contribution of wholesale and retail contamina- 
tion to the retail case life of rib steaks. This was accomplished by selecting 
wholesale ribs with varying degrees of surface contamination and fabricating 
rib-eye steaks using extremes of retail processing sanitation. The results 



- 9 



showed that a much greater amount of the variability in steak case life could 
be attributed to wholesale rib bacterial counts (45%) than the level of 
bacterial contamination on retail processing equipment (25%). In addition, 
wholesale rib contamination was found to be more than one and one half times 
as important as retail sanitation in determining retail beef case life. These 
findings do not negate the necessity of hygienic retail processing, but rather 
stress the need for improved sanitation throughout all levels of pre-retail 
processing. Conceivably, a conscientious retailer, employing strictly hygienic 
processing procedures, could fabricate retail cuts of inferior bacterial quality 
and reduced case life as a consequence of highly contaminated wholesale product. 

The results of these laboratory simulated retail processing experiments 
also allows the derivation of an equation which should have practical applica- 
tion in predicting the retail case life of beef: 

2 
Retail Case Life = 3.97 - 0.19 (log bacteria/cm on wholesale ribs) 

-0.14 (log bacteria/cm on retail processing equipment) 

The numbers of bacteria determined on the surface of ribs and retail equipment 
are converted to common logarithms prior to applying the equation. 

With knowledge of the level of retail sanitation and the bacterial quality 
of meat received by the retail outlet, retail case life could be predicted. 
Furthermore, this predictive equation would give the retailer some basis for 
quality control. Relative to this, by determining the retail case life of beef 
and the level of retail processing sanitation the above equation could be used 
by the retailer to assess the bacterial quality of product received from 
different suppliers. Subsequent beef purchases could then be directed towards 
suppliers providing product with lowest bacterial counts. 

Temperature 

Once retail beef cuts are overwrapped in the routinely used polyvinyl films 
and placed on display in the retail case, no further bacterial contamination is 
possible. At this point, it is the rate at which the resident bacteria grow 
that determines case life. Of the factors influencing bacterial growth, tempera- 
ture is the most critical. Although beef spoilage bacteria are capable of 
growth, at a limited rate at 0°C, their growth rate increases rapidly with small 
increments in temperature and becomes optimal at about 25°C. The growth rate of 
a typical beef spoilage bacteria can double as the temperature of incubation 
increases from 1 to 5°C and can triple with a further increase to 10°C. 
Increased bacterial growth means reduced case life. In Fig. 7, the importance 
of temperature to the retail case life of rib steaks is clearly illustrated. 
Although at steak temperatures approaching 0°C a retail case life of about 
8 days can be achieved, for each 1°C increase in temperature there is a coinci- 
dent 0.63 day decrease in case life. 



- 10 - 



7- 



6 



< 

Q 

- 5 



4- 



3 



2 



1 5 3 4 4 6 7 8 9 10 11 12 

STEAK SURFACE TEMPERATURE (C) 



Fl g , 7 . The retail case life of steaks is directly related to the steak sur- 
face temperature. 



Since the retail case life of beef is directly related to storage tempera- 
ture a means of display is necessary which maintains low temperatures but at 
the same time allows visual evaluation of the cuts by the consumer. This is 
accomplished in most retail outlets by overwrapping beef in an oxygen permeable, 
polyvinyl wrap and displaying in open, refrigerated cases illuminated with 
sufficient lighting to enhance the meat appearance. Most display cases are 
horizontal or vertical, fan-assisted, convection type cabinets where air is 
cooled by passage over evaporator coils and then blown over the display case 
through ducts. The temperature of the display case is monitored by thermometers 
situated directly in front of the incoming blower air. In our laboratory, a 
commercially available, horizontal fan-assisted convection type retail case is 
used in studies of retail beef case life. The retail case operates at a mean 
blower temperature of -0.5°C and a case life of 2-3 days is usually observed 
for steaks on display. This temperature and case life are close to average 
values reported from surveys of retail outlets. Although this retail display 
temperature should be more than adequate for the preservation of beef quality it 
was noted that when steaks were stored in a walk-in cooler at a slightly higher 
temperature (1°C), case life was substantially extended to more than 9 days. The 



- 11 - 



deterioration in retail acceptance of steaks on retail display is compared to 
that of steaks stored in the cooler in Fig. 8. Clearly, the acceptability of 
steaks on retail display deteriorated much more rapidly when compared to 
those stored in a walk-in cooler. Although the appearance of steaks on display 
remained acceptable for only 3 days, those in the cooler were still visually 
acceptable after 9 days of storage. The reduced case life of retail displayed 
steaks was found to result from a more rapid growth of psychrotrophic bacteria 
on the steak surface. 



extremely 

desirable 

7-»o — 



LU 

u 

z 
< 

Q. 

LU 

u 
o 

< 




r 

2 4 6 8 

xtremely STORAGE TIME (DAYS) 
ndesirable 



Fig. 8 . When steaks are stored in a walk-in meat cooler (■■——■ — -) they remain 
acceptable for a longer period of time when compared to steaks in a 
retail display case ( «^^^^") . 



These findings, at first glance, seem somewhat surprising since the actual 
temperature recorded at the retail case blower was slightly lower than that of 
the cooler. However, it should be stressed that retail case thermometers are 
a measure of the incoming blower air and do not necessarily reflect the tempera- 
ture of the displayed meat. To establish the temperature of steaks, thermo- 
couples can be used to continuously monitor fluctuations in steak surface tem- 
perature during retail display. A typical steak surface temperature profile 
for a 24 hour period of retail display is depicted in Fig. 9. It is immediately 
apparent that the actual surface temperature of steaks on retail display is 



- 12 



much higher than that recorded at the blower thermometer. In this particular 
case, the blower thermometer indicated a temperature of -0.5°C while displayed 
steak surface temperatures were on the average about 8°C higher (7.3°C). 
However, steaks stored in the walk-in cooler at 1°C did maintain a temperature 
of 1°C throughout the storage interval. These observations elucidate the 
unusual nature of the findings reported in Fig. 8. That is, the steaks stored 
in the walk-in cooler remained acceptable for a much longer period of time 
since they were maintained at a substantially lower temperature than steaks in 
the retail cabinet. 



18 



16 



-04 

o 



:«- 



;io 



i= 8 



6 



mean blower temp. = -0.5 C 
mean steak temp. = +7-3 C 




/ 




10 12 14 16 18 20 22 24 

TIME (HOURS) 



Fig. 9 . The actual temperature at the surface of steaks on retail display 
exceeds that measured by the retail case thermometer. 



In consideration of these findings one wonders as to why the temperature 
of beef in the retail case is excessively high and exceeds that measured by 
the blower thermometer. Part of the reason can be found in Fig. 9. At 
regular 12 hour intervals the retail case automatically defrosts and at this 
time steak surface temperatures can approach 17°C. Another important con- 
sideration is the intensity and duration of display illumination. The display 
case in the studies described herein was illuminated with 150 watt incandescent, 
cool-beam floodlights to give a light intensity of about 80 foot-candles at the 
meat surface. Lighting was automatically timed to illuminate the display case 
for 12 hours/day. In Fig. 9, the display case lighting was activated at hour 
8 and the display case remained illuminated until hour 20. During this 12 
hour period of illumination steak surface temperatures were found to be higher 
than in the absence of illumination. This is a type of "greenhouse effect" Ln 
that the heat produced by radiant energy is absorbed by the meat and trap' 



13 - 



between the polyvinyl wrap and the meat surface. Thus, although display illumi- 
nation enhances the appearance of beef it is detrimental to keeping quality. 

Apart from defrost cycles and illumination, other factors influencing the 
temperature of beef on display include fluctuations in room temperature, dis- 
play case design and the position of meats within the case. For example, 
products located near the blower or at the bottom of a horizontal case will be 
cooler than those displayed farther from the blower and nearer the load line. 
The combined influence of these factors accounts for the large discrepancy 
between retail display temperature and that recorded at the surface of beef on 
retail display. 

Although the temperature of retail beef should be maintained as close to 
0°C as possible for maximum keeping quality, displayed steaks are subjected to 
relatively abusive temperatures and under these conditions case life rarely 
exceeds 2 to 3 days. Some believe, that as a result of display case design and 
environment it may not be possible to maintain lower storage temperatures. 
However, in the laboratory, two studies were conducted to evaluate methods of 
increasing bacterial quality and beef case life through improved temperature 
regulation. 

Methods of Retail Temperature Control 

As shown earlier, bacterial growth can be reduced and steak case life can 
be extended by 6 days if the meat is stored at 1°C in a cooler. However, this 
is not a practical method of storage since it precludes consumer evaluation of 
appearance which is a necessary prerequisite to purchase. The possibility of 
reducing the time of retail display was therefore considered. This was accom- 
plished by removing steaks from display at the end of each work day, placing 
them in a cooler at 1°C and then returning product to the retail case each 
morning. In this manner, retail case defrosting was avoided and steaks were 
only subjected to the detrimental influences of the display environment for 8 
hours/day. The results of these investigations are shown in Fig. 10 and 11. 
Initially, bacterial growth on steaks continuously displayed was compared to 
that on steaks limited to 8 hours of retail display/day (Fig. 10). The results 
showed that reducing the time of retail display reduced the rate of bacterial 
growth and resulted in a 100 to 1,000 fold reduction in the bacterial load. 
Consequently, steaks with limited periods of retail display remained acceptable 
for a longer period of time than steaks held continuously in the retail case 
(Fig. 11) . Retail case life determinations revealed that case life could be 
extended by 2 days by overnight refrigeration in a walk-in meat cooler. These 
results establish a practical method by which a retailer could improve beef 
case life and reduce spoilage losses. 



- 14 - 



10* 



10 



10 



10 



10 



4 
10 



10 



10 



/ 



/ 



y 



/ 



/ 



s' •——• 24 h of retail display/ day 
o o 8h Of retail display/day 



2 3 

DME(DAYS) 



Fig. 10 . When steaks are limited to 8 hours of retail display per day 

(■■■' , ) by storage in a meat cooler overnight, psychrotrophic 
bacterial growth is retarded when compared to steaks remaining in 
the retail case ( ) . 



- 15 - 



< 

(/) 4 




• 24 h of retail display/day 
8h of retail display/day 



2 3 

TIME (DAYS) 



Fig. 11 . When steaks are limited to 8 hours of retail display per day 

(■-- ) by storage in a meat cooler overnight, they remain 
acceptable for a longer period of time when compared to steaks 
remaining in the retail case ( < ■ ) . 



- 16 - 



A second approach taken was to investigate the relationship between 
retail case temperature, bacterial growth and steak case life in attempt to 
determine a retail temperature setting which would improve product quality. 
In this regard, it was felt that retail cases may not be operating at levels 
which would provide adequate temperature control of displayed product. The 
results of this investigation are presented in Table 1. Retail case blower 
temperature and corresponding steak surface temperatures were monitored at 5 
distinct retail case temperature settings. Initially, it is evident that the 
actual retail case temperature setting is somewhat lower than that indicated 
by the blower thermometer (Table 1) . Of more importance, the surface tempera- 
ture of retail displayed steaks was on the average about 9°C higher than the 
temperature recorded by the blower thermometer. 



Table 1. The effect of retail case temperature on bacterial growth and steak 

case-life. A simple adjustment of the retail case temperature setting 
can reduce bacterial growth and substantially improve keeping quality 



Bacterial 
Growth Steak 

Rate Shelf Life 



Case 






Temperature 


Blower 


Steak 


Setting 


Temperature 


Temperature 


(C) 


(C) 


(C) 


-9.4 


-8.6 


1.9 


-6.7 


-5.7 


4.2 


-3.9 


-3.6 


5.3 


-1.1 


-0.5 


7.3 


+1.7 


+2.0 


11.8 



(Generations/h) (Days) 



0.09 8.2 

0.11 6.0 

0.14 5.6 

0.17 3.8 

0.28 1.9 



It should be stressed, that although the retailer may maintain a completely 
acceptable blower temperature of 2°C, the actual temperature of the product is 
closer to 12°C. As the temperature of the blower air is reduced from +2°C to 
-8.6°C there is a concomitant reduction in steak surface temperature, bacterial 
growth and consequently a more than 6 day increase in steak case life. These 
results indicate that a relatively simple adjustment of blower temperature by 
the retailer can result in a retail case life for beef which exceeds one week. 
Further studies are necessary to determine whether the economic benefits of 
reduced spoilage losses would compensate for increased refrigeration costs. 

This review has summarized the results of current research on the growth 
and spoilage potential of bacteria and the importance of sanitation and tempera- 
ture to the bacterial quality of retail beefo The two practical methods of 
retail temperature control described should be of direct economic benefit to 
the retail beef industry by reducing spoilage losses. 



U8RARY / BIBLIOTHEQUE 



AGRICULTURE CANADA OTTAWA K IA 0C5 

3 T073 000303A1